Heating by circulating heat-transferring liquids



Aug. 15, 1933. R. THURM 1,922,509

HEATING BY CIRCULATING HEAT TRANSFERHING LIQUIDS Filed OCt. 28, 1929 Sodium metal alloy.

WMW.

INVENTOR Patented Aug. 15, 1933 UNITED STATES PATENT OFFICE" HEATING BY CIRCULATING HEAT-TRANS- FERRING LIQUIDS Richard Thurm, Saginaw, Mich., assignor to Baker Perkins Company,

Inc., Saginaw,

This invention relates to heating systems, in which the heat of the furnace is transferred to the room, apparatus or objects to be heated by means of suitably arranged closed, endless pipes, tubes or the like containing a heat-transferring liquid circulated in the latter by gravity or mechanical means.

Inapparatus of this kind water is commonly used. l at the low critical temperature of water 365 C.=689 F.,makes it practically ineffective, for a temperature higher than that named, and it's high internal pressure, the consequence of its low critical temperature, makes it unsafe, if temperatures near this point are required.

To overcome this drawback other liquids, mostly organic compounds, having a high boiling point have been proposed for this purpose, but they decompose gradually, and the higher the temperature, the quicker, and have a low heat conductivity. For these reasons such organic liquids failed to be more generally used as heattransferring liquid in apparatus of this kind.

Mercury, which has a boiling point of about 360 C.=680 F., has also been recommended, but its high specific gravity 13.59 and high price prevented its general use.

I have now found that for gravity as well as for forced circulation heating systems pure alkali metals and especially their liquid alloys with each other form suitable and advantageous circulating and heat-transferring mediums in all such systems. It is therefore an object of my invention to provide a closed circulating heating system having as a heat transferring medium an alloy composed of potassium and sodium metal.

It is a still further object of my invention to provide a closed circulating heating system in which the heat transference medium shall have a high boiling point, low pressure, high thermal conductivity, great resistance to decomposition at high temperatures, lightness in weight and great economy of use.

Potassium and sodium, which, for their comcomparatively low price, alone come here in question, are solid at ordinary temperature. Potassium melts at 625 C.=144.5 F., boils at 720 0.: 1328 F. and has a specific gravity of 0.86 and specific heat of 0.165. Sodium melts at 955 C.=172.9 F., boils at 742 C.=1367.6 F. and has a specific gravity of 0.973 and specific heat of 0.28. As potassium and sodium solidify, when the apparatus is cooled down to ordinary temperature, it is advisable to keep it warm, while the operation is interrupted for some time. This precaution is not needed, when the liquid alloys of potassium and sodium are used; for instance I preferably employ alloys composed of 50-75% potassium and 50-25% sodium.

An alloy of 50% potassium and 50% sodium melts at 6 C.=42 F., and an alloy of 75% potassium and 25% sodium at -10 C.=14 F.

The boiling point of these alloys lies between 720 and 800 C.=1328 and 1472 F.

The low specific heat of the alkali metals and their alloys with each other makes for gravity heating systems a larger diameter of the pipes used therein necessary, than that required in the same kind of system, in which the pipes are filled with water. Referring to the drawing, the single figure represents diagrammatically a closed circulating heating system in which 1 is the usual furnace, either fluid or solid fuel fired, having therein the usual heating coils 2, riser 3, and heat radiator 4, which transmits heat to the device to be heated 5. 6 is the return line, and 7 is the expansion tank. As a heat transference medium I use an alloy of potassium metal and sodium metal, preferably in the proportions of 50 to 75% potassium metal, and 50 to 25% sodium metal, which, in these proportions, are liquid at ordinary temperatures.

It will be understood, that using alkali metals or their alloys with each other as heat-transferring circulating liquid in heating systems, the pipes, tubes and the like of the latter must be absolutely dry and in their interior as free as possible of any oxides, and that, after having received their due charge of the alkali metal or alloy they are closed immediately. I evacuate the apparatus before charging and fill and close it hermetically under vacuum.

The high heat conductivity of the alkali metals and their alloys with each other, the absence of internal pressure below a temperature of 720 C. 1328 F. in heating systems, in which they are used as circulating heat-transferring liquid, and their practical indestructibility under normal conditions of such systems give them an extraordinary advantage over the liquids used hitherto for the same purpose and make it possible to solve many heating problems still unsolved.

I claim:

1. A heating system comprising suitably arranged closed endless pipes, a heat transference medium in said pipes composed of an alloy of potassium metal and sodium metal and means to heat said heat transference medium.

2. A heating system comprising suitably arranged closed endless evacuated pipes, a heat transference medium in said evacuated pipes,

said heat transference medium composed of an alloy of potassium metal and sodium metal and means to heat said heat transference medium.

3. A heating system comprising suitably arranged closed endless pipes, a heat transference medium in said pipes composed of an alloy of 50 to potassium metal and 50 to 25% sodium metal, and means to heat said heat transference medium.

RICHARD THURM. 

